Terminal assembly for a coaxial cable

ABSTRACT

A terminal for a coaxial cable includes an electrically conductive core mounted in a dielectric member. The dielectric member along with the conductive core are positioned within an electrically conductive ground shield. The ground shield includes two identical split-barrel housing members which are joined together. When joined, the housing members form a cylindrical channel having surfaces which intimately contact an exposed length of cable outer conductor layer, creating a conductive connection between the outer conductor layer and the ground shield and structurally maintaining the outer conductor layer concentric to the dielectric sheath and inner conductor of the cable.

TECHNICAL FIELD

The present invention relates to electrical terminals for connection tocoaxial cable and more particularly relates to a terminal having atwo-piece ground shield.

BACKGROUND OF THE INVENTION

A typical coaxial cable for signal transmission includes a centerconductive core or inner conductor surrounded by an inner dielectricsheath. An outer conductor or conductive shield surrounds the innerdielectric sheath and typically is a metal braid. The conductive shieldis surrounded by an outer dielectric sheath of the cable.

Electrical terminals are known for terminating a coaxial cable so thatthe cable can be connected to another connecting device, such as acomplementary mating connector, a printed circuit board, and the like.Such terminals typically include a core conductor or contact formechanically and electrically connecting to an end of the innerconductor of the cable, a dielectric sleeve therearound, and an outerconductor or ground shield for mechanically and electrically connectingto the outer conductor of the cable.

The terminal must be configured and connected to the coaxial cable insuch a manner as to minimize voltage standing wave ratio (VSWR),insertion losses, and radio frequency (RF) leakage. Commonly, thelargest component of insertion loss is reflection due to impedancediscontinuities. Energy reflected at impedance discontinuities does notreach the load. Such discontinuities result from variations in theradial distance between the outer surface of the inner conductor and theinner surface of the outer conductor. Such discontinuities includechanges in diameter in either conductor or deformation of eitherconductor. RF leakage results from radiation loss through holes or seamsin the terminal or cable.

Electrical and mechanical connection of the core conductor of theterminal to the inner conductor of the cable is commonly established byaxially inserting the inner conductor into the core conductor and thenradially crimping and/or soldering the core conductor of the terminal tothe inner conductor of the cable. It is also common for such electricaland mechanical connection of the ground shield to the outer conductor ofthe cable to be established by a method that includes stripping the endof the coaxial cable, sliding a ferrule onto the cable, folding theouter conductor braiding back over the outer dielectric sheath,inserting the stripped end of the coaxial cable into the ground shield,unfolding the braiding over the ground shield, sliding the ferrule overthe braiding and ground shield, then crimping the ferrule to thebraiding thereby pressing the braiding against the ground shield.

U.S. Pat. No. 3,854,003 to Duret discloses a ground shield terminalassembly comprising two elastic half-shell conductive housing membershaving chamfered ends. The assembled housing members are surrounded by athreaded metallic sleeve which enables a nut to cooperate with thethreads to press a ring having an inclined surface over the chamferedends to deform the housing members, thereby pressing them against theouter conductor of a coaxial cable.

Such known methods for assembling a terminal to a coaxial cable arelabor intensive and technique sensitive. These methods requiresignificant manual manipulation of the shielding braid which deforms theouter conductor causing reflection and insertion loss. Crimping alsodeforms the outer conductor causing reflection and insertion loss.Variation in assembly technique impacts the integrity of the connectionand results in variation in performance.

Known coaxial cable connectors commonly include a threaded, cylindricalground shield which has an axially extending bore. These known groundshields commonly include plating on outside surfaces and on insidesurfaces which define the bore. It is difficult to apply a uniformplating to inside surfaces of such a design. Plating voids therebyresult which increase reflection and leakage losses.

As the use of high frequency systems such as digital satellite radio,Global Positioning Systems (GPS), cell phones, and mobile televisioncontinues to grow there is an increasing need for coaxial cableconnectors which meet the radio frequency performance needs of suchsystems, offer consistent performance, and are easy and inexpensive toassemble.

SUMMARY OF THE INVENTION

The present invention provides advantages and alternatives over theprior art by providing a terminal for connection to a coaxial cable,together with a ground shield and a method for assembling the groundshield to a coaxial cable. The terminal comprises a two-piece groundshield capable of being connected to an outer conductor of the cablewithout the need to deform the outer conductor either by dressing itover the ground shield or by crimping it to the ground shield.Importantly, the terminal is capable of being used to carry highfrequency signals such as those used by communication and entertainmentsystems in automotive and other applications.

According to a preferred embodiment of the present invention disclosedherein, a terminal assembly for a coaxial cable is provided whichincludes a ground shield with surfaces defining an internal passageway.In the preferred embodiment, the ground shield includes a strain reliefportion having protruding ribs for engaging an outer dielectric sheathof the coaxial cable and a contact portion for electrically andmechanically bonding an outer conductor of the coaxial cable to theground shield. As a result, it is not necessary to crimp the outerconductor to the ground shield.

In the preferred embodiment, the ground shield is comprised of twoidentical shield halves joined at a plane extending along an axis of theinternal passageway. Each of the shield halves is constructed using adie cast process enabling strain relief features, internal componentretention features, and shapes that optimize radio frequency performanceto be easily produced. The two-piece design enables the ground shield tohave a uniform plating. Each of the shield halves is easier to reliablyplate than a complete shield having a bore.

A method is provided for assembling the ground shield of the presentinvention to a coaxial cable. The method enables automated assembly ofthe ground shield to the cable.

These and other features and advantages of the present invention willbecome apparent from the following brief description of the drawings,detailed description, and appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described, by way of example, withreference to the accompanying drawings, in which:

FIG. 1 is an exploded perspective view of a preferred embodiment of aterminal according to the present invention;

FIG. 2 is a side elevation view of a coaxial cable with various internallayers exposed;

FIG. 3 is a perspective view of the terminal of FIG. 1;

FIG. 4 is a view taken along line 4-4 of FIG. 3;

FIG. 5 is a flow diagram of a method of the present invention; and

FIG. 6 is an exploded perspective view an aspect of the terminal of FIG.1, but with a cable in place to illustrate the elements identified inFIG. 5.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the figures wherein like numerals refer to like elementsthroughout the several views, FIGS. 1, 3, and 4 illustrate a preferredembodiment of an electrical terminal 10 of the present invention. Theterminal 10 includes an electrically conductive core conductor 12, adielectric member 14, a conductive ground shield 16, and a split ringsupport 18. The ground shield 16 is an assembly of two identical groundshield halves or housing members 20 a, 20 b. When joined, the groundshield housing members 20 a, 20 b define the completed ground shield 16.Each ground shield housing member 20 a, 20 b is preferably a rigid diecast member constructed of a nickel plated zinc alloy.

FIG. 2 illustrates a coaxial cable 200 which includes an inner conductor202, an inner dielectric sheath 204 around the inner conductor 202, anouter conductor layer 206 having a cylindrical outer surface andconcentrically surrounding the inner dielectric sheath 204 and the innerconductor 202, and an outer dielectric sheath 208 around the outerconductor layer 206. The coaxial cable 200 is shown stripped back withan exposed tip of the inner conductor 202, an exposed axial length ofthe inner dielectric sheath 204, and an exposed axial length of theouter conductor layer 206.

Referring back to FIGS. 1, 3, and 4, the core conductor 12 includes abody portion 30 and a contact portion 32. Preferably, the core conductor12 is formed from sheet metal which is preferably gold plated brasswhich is stamped and then rolled to form the generally cylindrical shapeof the core conductor 12. The contact portion 32 includes two springmembers 34 which extend from the body portion 30 and terminate at distalends 36. The spring members 34 have opposing surfaces which define apin-receiving bore 38. The body portion 30 includes an inner surfacewhich defines an inner conductor receiving bore 40.

The dielectric member 14 has a generally cylindrical shape and ispreferably made of Teflon or a material comparable to the innerdielectric sheath 204. An inner surface 50 of the dielectric member 14defines an axially extending bore 52. The inner surface 50 includes afirst portion 54 for containing the body portion 30 of the coreconductor 12. An annular gap 118 extends between the first portion 54 ofthe inner surface 50 of the dielectric member 14 and body portion 30 ofthe core conductor 12 to allow room for protrusions (not shown) in thebody portion 30 caused by crimping. The inner surface 50 also includes asecond portion 56 for retaining the contact portion 32 of the coreconductor 12. The inner surface 50 further includes a third portion 57which surrounds the spring members 34 of the core conductor 12. Theinner surface 50 of the dielectric member 14 holds the core conductor 12in axial alignment within the terminal 10. The dielectric member 14further includes an outer surface 58. The outer surface 58 includes alarge diameter portion 60, a reduced diameter portion 62, and atransition portion 64 therebetween. The outer surface 58 also includesan annular groove 66.

The ground shield 16 includes an inner surface 70 and an outer surface72. The inner surface 70 defines an axially extending passageway 74. Theground shield 16 includes a rearward strain relief portion 76 forcontact with the outer dielectric sheath 208 of the coaxial cable 200, acontact portion 78 for electrical connection with the outer conductorlayer 206 of the coaxial cable 200, a support portion 80 which retainsthe dielectric member 14, and a forward mating portion 82 for connectionwith a complementary ground of a mating connector (not shown). Each ofthe two ground shield housing members 20 a, 20 b generally have a splitbarrel shape and are aligned along a plane P of separation runningparallel to a longitudinal axis A of the ground shield 16. The groundshield 16 includes an enlarged rearward outer portion 84 which serves asa processing aid. Enlarged diameter portions 86 on a mid-portion of theouter surface 72 align with features on a complementary coaxial cableconnector housing (not shown).

The inner surface 70 of the strain relief portion 76 includes aplurality of spaced strain relief ribs 88 each extending partiallyaround a circumference of the inner surface 70 for gripping the outerdielectric sheath 208 of the coaxial cable 200.

The contact portion 78 of the inner surface 70 of the ground shield 16is shaped to intimately match the shape of the outer surface of theexposed length of the outer conductor layer 206. When the ground shieldhousing members 20 a, 20 b are joined together over the exposed lengthof the outer conductor layer 206, a conductive connection is createdbetween the ground shield 16 and the outer conductor layer 206. Theinner surface 70 of the ground shield 16 structurally maintains theouter conductor layer 206 concentric to the dielectric sheath 204 andthe inner conductor 202 without the need to deform the outer conductorlayer 206 either by dressing it over the ground shield 16, by crimpingit to the ground shield 16, or by tightening the ground shield 16 aroundthe outer conductor layer 206.

In the preferred embodiment, a conductive bonding agent 90 is disposedon the contact portion 78 of the inner surface 70 of the ground shield16 and the outer conductor layer 206 of the coaxial cable 200. Solder isthe preferred bonding agent. However, conductive epoxy or other bondingagents may also be used. The conductive bonding agent 90 bonds the outerconductor layer 206 to the ground shield 16 and fills in voids anddiscontinuities between the outer conductor layer 206 and the groundshield 16. The conductive bonding agent 90 also bonds the first groundshield housing member 20 a to the second ground shield housing member 20b. At a distal end 207 of the exposed axial length of outer conductor206, the inner surface 70 of the ground shield transitions to a firstreduced diameter portion 91. The exposed axial length (shown at 92) ofinner dielectric 204 presses against the first reduced diameter portion91 of the ground shield 16 preventing the conductive bonding agent 90from contacting the exposed axial length of inner conductor 202 or thecore conductor 12. An aperture 94 extends through the contact portion 78of each ground shield housing member 20 a, 20 b enabling visualinspection of the conductive bonding agent 90.

In some alternate embodiments, no conductive bonding agent 90 is usedand the ground shield housing members 20 a, 20 b are joined together bywelding, by form fit, or by another attachment mechanism known to thoseskilled in the art. Once so attached, the inner surface 70 of the groundshield 16 intimately contacts the exposed layer of outer conductor layer206 providing an electrical connection between the ground shield 16 andthe outer conductor layer 206.

The dielectric support portion 80 includes a second reduced innerdiameter portion 96 which surrounds the reduced diameter portion 62 ofthe dielectric member 14. The dielectric support portion 80 alsoincludes an annular rib 98 on the inner surface 70 for engaging theannular groove 66 in the dielectric member 14.

The forward mating portion 82 includes four spaced contact beams 100which extend forwardly from the dielectric support portion 80. Insidesurfaces of the four contact beams 100 form an opening 102 for receivinga complementary mating ground shield (not shown). The split ring support18 extends around the outside surface of the contact beams 100 toprovide a normal force when a complementary ground (not shown) is matedto the ground shield 16.

Prior to assembly, each ground shield housing member 20 a, 20 b definesan axially extending open-ended trough or channel 104. The channel 104has an open side such that a cross-section of the channel 104 formssubstantially one-half of a cylindrical surface of the passageway 74. Inthe preferred embodiment, each ground shield housing member 20 a, 20 bincludes a coating 106 of the conductive bonding agent 90 disposed onthe channel 104 surface in an area that forms the contact portion 78 ofthe completed ground shell 16. The coating 106 is preferably a solderpaste. Alternately, other conductive coatings or claddings can be used.Each ground shield housing member 20 a, 20 b can also be providedwithout a coating 106 or cladding.

Each of the ground shield housing members 20 a, 20 b include mateable,integral attachment members which include a protruding rail 108 and acomplementary slot 110 which extend longitudinally along opposing edges112, 114 of each ground shield housing member 20 a, 20 b. When thehousing members 20 a, 20 b are assembled into the completed groundshield 16, the rail 108 and the slot 110 are positioned such that therail 108 on each ground shield housing member 20 a, 20 b is received inthe slot 110 of the other ground shield housing member 20 b, 20 a. Inthe preferred embodiment, a notched portion 116 of channel 104 providesroom for a braiding of the outer conductor layer 206 to fan out. Thishelps to prevent a loose braiding strand from lodging between the twoground shield housing members 20 a, 20 b.

FIGS. 1, 3, and 4 illustrate a female configuration of the terminal 10of the present invention. Male configurations of the terminal of thepresent invention may also be produced in a manner well known to thoseskilled in the art.

Referring now to FIG. 5, a flowchart 300 illustrates a preferredembodiment of a method for electrically connecting the ground shield 16to the coaxial cable 200. FIG. 6 illustrates the terminal 10 along withthe coaxial cable 200 to depict the elements identified in the flowchartof FIG. 5. Referring back to FIG. 5, in step 302 the coaxial cable 200is provided including an inner conductor 202, an inner dielectric sheath204 around said inner conductor 202, an outer conductor layer 206 havinga cylindrical outer surface and concentrically surrounding said innerdielectric sheath 204 and inner conductor 202, and an outer dielectricsheath 208 around said outer conductor 206.

In step 304, an end portion 210 of the coaxial cable 200 is strippedleaving an exposed tip of inner conductor 202, an exposed axial lengthof inner dielectric 204, and an exposed axial length of outer conductorlayer 206. Optionally, the end portion 210 of the coaxial cable 200 maybe stripped without leaving the exposed axial length of inner dielectric204. However, it is preferable to have an exposed axial length of innerdielectric 204 to prevent the conductive bonding agent 90 fromcontacting the exposed inner conductor 202.

In step 306, the conductive ground shield 16 is provided, the groundshield 16 includes the first housing member 20 a and the second housingmember 20 b, each of the housing members 20 a, 20 b includes a channel104 defined by a substantially half cylindrical surface having a contactportion 78 which intimately matches the shape of the exposed axiallength of the outer conductor layer 206, each of the housing members 20a, 20 b also include mating, integral attachment members capable ofbeing joined together to form the channels 104 into a complete cylinder.Preferably, the mating integral attachment member includes theprotruding rail 108 and the complementary slot 110 which extendlongitudinally along the opposing edges 112, 114 of each ground shieldhousing member 20 a, 20 b. Each rail 108 fits closely within arespective slot 110. The channel 104 of each housing member 20 a, 20 bmay also include the coating 106 of conductive bonding agent 90 providedin the contact portion 78 of each of the housing members 20 a, 20 b.

In step 308, the end portion of the coaxial cable 200 is placed into thechannel 104 of the first housing member 20 a, aligning the exposed axiallength of the outer conductor layer 206 with the contact portion 78.

Then, in step 310, the second housing member 20 b is placed in contactwith the first housing member 20 a mating the integral attachmentmembers which preferably include the rail 108 and the complementary slot110. The channels 104 thereby form a cylinder surrounding andelectrically contacting the exposed axial length of outer conductorlayer 206. The contact portion 78 of the second housing member 20 baligns with the exposed axial length of the outer conductor layer 206.In a preferred embodiment of the method, the coating 106 of theconductive bonding agent 90 is provided in the contact portion 78 ofeach of the housing members 20 a, 20 b, and the conductive bonding agent90 is heated until it flows between the housing members 20 a, 20 bforming a both a mechanical bond between the housing members 20 a, 20 band the conductor layer 206 between when the conductive bonding agent 90cools. Bonding agent 90 can also flow into the seam between the housingmembers 20 a and 20 b and directly mechanically bond them together. Alsoin the preferred embodiment of the method, the conductive bonding agent90 is heated in the same heating step until it flows between the housingmembers 20 a, 20 b and the outer conductor layer 206 forming aconductive bond between the housing members 20 a, 20 b and the outerconductor layer 206 when the conductive bonding agent cools. In analternate embodiment, each of the housing members 20 a, 20 b areprovided with corresponding form fit features, and the two housingmembers 20 a, 20 b are mechanically attached by pressing the two housingmembers 20 a, 20 b together. In another alternate embodiment, the twohousing members 20 a, 20 b are attached using a welding process. In yetanother alternate embodiment, a bonding agent such as solder is injectedinto the passageway 74 or otherwise applied to the housing members 20 a,20 b to bond them together.

This invention has been described with reference to a preferredembodiment and modifications thereto. Further modifications andalterations may occur to others upon reading and understanding thespecification. It is intended to include all such modifications andalterations insofar as they come within the scope of the invention.

1. A terminal for an end of a coaxial cable, said coaxial cable including an inner conductor, an inner dielectric sheath around said inner conductor, an outer conductor layer having a cylindrical outer surface and concentrically surrounding said inner dielectric sheath and inner conductor, and an outer dielectric sheath around said outer conductor, and in which said coaxial cable end has been stripped back to expose a tip of said inner conductor, an axial length of said inner dielectric sheath, and an axial length of said outer conductor layer outer surface, said terminal comprising: an electrically conductive core conductor for electrically connecting with said inner conductor of said coaxial cable; a dielectric member having a body for receipt therein of said core conductor, wherein said dielectric member comprises a material comparable to said inner dielectric sheath; a ground shield comprising first and second electrically conductive housing members, each said housing member including a channel comprising a substantially half cylindrical surface intimately matching the shape of the exposed length of outer surface of said cable outer conductor layer, wherein each of said housing members also includes first and second mating, integral attachment members capable of being joined together to thereby form said channels into a complete cylinder, whereby, when said ground shield housing members are joined together, said channel surfaces intimately contact said exposed length of outer conductor layer, creating a conductive connection between said outer conductor layer and said ground shield and structurally maintaining said outer conductor layer concentric to said dielectric sheath and said inner conductor.
 2. The terminal of claim 1, further comprising a conductive bonding agent disposed between said ground shield and said exposed length of outer conductor layer, wherein said conductive bonding agent comprises epoxy.
 3. A ground shield for an end of a coaxial cable, said coaxial cable including an inner conductor, an inner dielectric sheath around said inner conductor, an outer conductor layer having a cylindrical outer surface and concentrically surrounding said inner dielectric sheath and inner conductor, and an outer dielectric sheath around said outer conductor, and in which said coaxial cable end has been stripped back to expose an axial length of said outer conductor layer outer surface, said ground shield comprising: first and second electrically conductive, rigid ground shield housing members, each said housing member including a channel comprising a substantially half cylindrical surface intimately matching the shape of the exposed length of outer surface of said cable outer conductor layer, said housing members capable of being joined together to thereby form said channels into a complete cylinder, whereby, when said ground shield housing members are joined together, said channel surfaces intimately contact said exposed length of outer conductor layer, creating a conductive connection between said outer conductor layer and said ground shield and structurally maintaining said outer conductor layer concentric to said dielectric sheath and said inner conductor, wherein said rigid ground shield housing members comprises a nickel plated zinc alloy. 